Effect of cellulase-assisted refining on the properties of dried and never-dried eucalyptus pulp

The effect of two different cellulases on the hornification phenomenon, in which drainability (Schopper-Riegler method) and mechanical properties diminish when pulps are dried, was studied. The enzyme applications tested included a commercial enzyme named ComC (Pergalase A40 from CIBA) and a laboratory enzyme from Paenibacillus sp. strain BP-23 named CelB. Industrial never-dried Eucalyptus globulus bleached kraft pulp was split in two halves and one of them was dried at ambient controlled conditions. We compared enzyme effects on both pulps (wet pulp and dried pulp) before and after PFI mill refining. Enzyme applications increased drainability (Schopper-Riegler method) and water retention value (WRV) of never-dried bleached pulp, although this did not imply an enhancement of the mechanical properties of paper. Cellulase treatment of dried pulps, by contrast, gave rise to increased drainability and WRV and also to improved mechanical properties. The changes caused by drying became less significant after enzyme application. Handsheets from CelB-treated dried pulps showed an improvement of tensile and burst indexes while tear decreased. The effect produced by CelB can be considered a biorefining step. In fact, by means of enzyme treatment with CelB the properties of paper manufactured from dried pulp equalled the properties attained from wet fibres, with the exception of tear index. Changes were also found in surface fibre morphology, such as flakes and peeling due to cellulase treatment. The surface modification of fibres with cellulases gives rise to better bonding properties and a closer structure of paper. The final conclusion is that treatment with cellulases could compensate the hornification effect and lead to an important saving of refining energy. The novel enzyme, CelB, was the most effective in improving paper properties and counterbalancing the hornification effect caused by drying.